I had a NutriBullet Pro 900, used it for 8 months, and recently sold it and bought a Vitamix.
The NutriBullet Pro 900 was a great starter machine.
I highly recommend it if you want to start to get into smoothies and don't want to drop the $400+ for a Vitamix.
That being said, I like the Vitamix a lot better.
While the NutriBullet 900 blended up fruits and veggies fine, the Vitamix is on another level, as it basically turns everything into a smooth juice. The Vitamix even chops through raspberry and blackberries seeds, leaving no trace of them.
I also like how the Vitamix container is twice the size of the Nutribullet, since I make HUGE smoothies.
As for which Vitamix to buy, it depends on if you want per-set programs, touchscreen, etc. They also recently changed cup sizes from tall and skinny to short and fat, as well as they've introduced a new motor. A lot of the models are the same, but have different names for different retailers.
After a bunch of research earlier this year, I ended up going with the most popular model (the one that has made Vitamix famous): the old motor with the tall and skinny cup, no presets. Just simple blending, with variable speed.
Also, Vitamix does a really, really good factory refurbished sales.
Something like this is great value (I have this model, and am really, really happy with it):/www.vitamix.com/Shop/Certified-Reconditioned-Standard?skuId=001811
edit: the factory refurbished have a 5 year warranty. The new ones have a 7 year warranty. FWIW, I remember reading somewhere that a guy who works for Vitamix said that 99% of these refurbished models have been used for less than 5 minutes... people think it's too loud or too big out of the box, and return it.
Post Edited (Mustard Seed) : 3/8/2017 1:13:46 PM (GMT-7)